The invention relates to a method for determining a confidence limit for telecommunication network elements, the method comprising the steps of: storing into a database the number of data transmission connections taking place through a network element during a predetermined period; determining a value for a variable describing the number of faulty operations in the network element in relation to the number of the data transmission connections; and setting a target value for the variable describing the relative number of faulty operations in the network element.
In large telecommunication networks, well-functioning network management systems are an important prerequisite for the reliability of network operations. The role of network management systems is particularly important in wireless telecommunication networks where the radio interface between a mobile station (MS) and a fixed network element, such as a base station (BTS), is usually the point where the data transmission connection is most unreliable and most susceptible to interference. As mobile communication networks become more common, increasing demands are naturally also set for extended coverage and higher capacity of the networks. This, in turn, increases the number of network elements managed by a network operator; large mobile networks may comprise several thousands of logical network elements.
This sets high requirements on the network management system. The network operator must be able to monitor and control the network capacity and the network elements preferably at one location. In addition, data on the network element operations, i.e. the load on the element, the types of data transmission that take place through the element, and any faults in the element, must be available at predetermined intervals. These data are stored into the database of the network management system and they are used for determining typical values for different indicators describing the operation of each element.
For poorly functioning network elements to be detected, the network operator sets threshold values for indicators describing various fault situations; depending on the indicator type, the indicator value may not be higher or lower than these threshold values in a normal situation. The accepted indicator values between the threshold values are referred to as the confidence interval. Separate confidence limits are defined for each indicator of each network element, and if the limits are exceeded, a notification is sent to the network management system. This allows different fault situations and poorly functioning network elements to be monitored.
A problem with the above arrangement is that the confidence limit to be set for each indicator is defined as a fixed value. At first, each network element type is typically given the same fixed confidence limit which the operator can change network-specifically, when needed. However, when a fixed confidence limit is used, special situations due to changes in traffic volumes cannot be taken into account. If a less busy network element is given the same confidence limits as a busy network element, even a minor exception from the normal number of faults may cause an error notification from the less busy network element because the number of fault situations is calculated as a percentage of the total traffic volume. Such an error notification is usually caused, more likely, by a statistical coincidence than a real failure in the network element. On the other hand, the setting of confidence limits separately for each network element and each hour is most laborious and requires detailed information about the different network elements and the traffic volumes transmitted through them.
An object of the invention is to provide a method allowing the above problems to be solved. The objects of the invention are achieved with a method which is characterized by setting a confidence limit to a target value, the deviation of the confidence limit from the target value changing in proportion to the number of data transmission connections.
According to a preferred embodiment of the invention, the target value is assigned a confidence limit, the deviation of the confidence limit from the target value becoming either smaller, due to an increase in the number of the data transmission connections, or larger, due to a decrease in the number of the data transmission connections. According to another preferred embodiment of the invention, data transmission connections taking place through the network element during a time unit are assigned a lower limit which must be exceeded before a confidence limit can be set for the target value. According to yet another preferred embodiment of the invention, for each hour of the day, a network-element-specific target value for a variable describing the number of faults in the network element and a confidence limit for the target value are determined, as well as a variable value describing the number of faulty operations in the network element per time unit during one hour.
The invention is based on setting a confidence interval for indicators describing faulty operations in the network elements, the length of the confidence interval being determined by the traffic volumes transmitted through the network element. Consequently, when the traffic volumes increase, the confidence interval becomes shorter, thus allowing quicker response to fault situations concerning busy network elements. When traffic volumes decrease, the confidence interval becomes longer which reduces the number of false alarms made by less busy network elements.
An advantage of the method of the invention is that it clearly improves the reliability of network management in the monitoring of network elements, because the confidence limits allow variations in traffic volumes to be taken into account better, which significantly reduces the number of false alarms. Furthermore, the method of the invention facilitates the operator""s work because all the information needed for determining the confidence limits is obtained on the basis of statistical data collected into the database, thus allowing the confidence limits to be determined automatically, without the network operator being required to have detailed information about the operational circumstances of each network element. According to a preferred embodiment of the invention, no laborious changes are required in the network management system for modifying the updating interval of the data to be collected into the database; it is sufficient that the values of the indicators are measured after each monitoring period. Another preferred embodiment provides a further advantage in that the network operator is informed about fault situations in network elements quicker than before.